Study And Control On Photodegradation Of Biodegradable Poly (butylene Adipate-co-Terephthalate) Films

The continuous accumulation of waste plastics in the environment causes serious ecological and environmental problems.Film products,which account for nearly 50%of the world's new plastic waste,are one of the main sources of "white pollution".Using biodegradable materials instead of traditional film resins,such as polyethylene,is the main method to control the "white pollution" of films.The biodegradable poly(butylene adipate-co-terephthalate)(PBAT)is an ideal material for thin film preparation,as it exhibits similar overall performance to that of low-density polyethylene.However,its application is limited by inherent weaknesses,such as poor weatherability and uncontrollable degradation period.Using the the density functional theory computations of photodegradation reactions,this study revealed the degradation mechanism of PBAT,guided the selection,design,and construction of photo-stabilizers,and explored the efficient weatherability modification method for PBAT.This knowledge allows preparation of biodegradable films with good weatherability and UV barrier capacity.In this dissertation,the difficulty of chain scission in Norrish I,II and photooxidation of PBAT,and the relationship between chain chemical structure and macroscopic properties of PBAT were first studied.This shed light on the dominant degradation reaction in PBAT photodegradation.The effects of different stabilizers on the chain structure,thermal and mechanical properties of PBAT in the accelerated aging process were then investigated,thus verifying its degradation mechanism.On this basis,a reactive light stabilizer TDET containing multiple epoxy groups was synthesized,and the mechanical,thermal,and weathering properties of PBAT/TDET composite films were studied.Fatty acid-modified lignins were blended with PBAT,following with the investigation of the aggregation structure,thermal,mechanical and weather resistance of the resulting composite films.Meanwhile,core-shell lignin/melanin nanoparticles were also prepared,where the aggregation,thermal,mechanical and UV resistance of PBAT nanocomposite films were investigated,which confirmed the synergetic effect between lignin and melanin on the UV absorption and weatherability.The main conclusions of this work are as follows:(1)Through density functional theory calculation,the energy barrier of each reaction leading to chain scission in PBAT photodegradation was clarified,allowing for the photodegradation mechanism of PBAT to be revealed.In addition,PBAT/photo-stabilizer composite films with significantly improved weatherability was developed through the incorporation of photo-stabilizers.(2)A hydroxyphenyl triazine compound TDET with multiple epoxy groups was designed and constructed.Its epoxies could covalently bond with the terminal carboxyl groups of PBAT in high-temperature processing,playing a dual role of photo-stabilizer and chain extender.(3)10-undecenoic and oleic acid were used for the modification of soda lignin to enhance its dispersion in PBAT.The resulting PBAT/modified lignin composite films maintained good mechanical properties when containing 20wt%lignin and had excellent UV barrier capacity and weatherability.(4)Lignin and melanin were combined in a core-shell nanoparticle with lignin core and melanin shell.The nanoparticles can endow PBAT film with good UV blocking efficiency and weather resistance while ensuring its optical transparency.